Supported platforms: CODESYS 2.3

 

PVC_AdaptiveController is in normal operation mode if:

• The control is enabled, i.e. i_Enable is TRUE AND

• The input parameters are valid and the inputs are inside in allowed limits AND

• Overcurrent or wire broken situation is not detected AND

 

In normal operation the function block adjusts the output o_PWMRatio so that the measured current i_CurrentMeasured achieves the requested current i_CurrentRequest. The measured current should achieve the request current as fast as possible.

 

The output PWM ratio is calculated from equation 1 (Ohm’s law)

 

 

, where RBasis is the base value for resistance

 

, where

CorrectionFactorArr[index] is the correction factor from array defined in application,

index = i_CurrentRequest / i_ParStep, and

CORRECTION_SCALING = 1000

 

, RPI is the PI-controller

 

, where

CurrentError = OldCurrentRequest-i_MeasuredCurrent, and

Integrator = PI-controller integrator term

 

, RImp is the startup impulse

 

Positive direction:

Negative direction:

, where

TargetCurrentChange = i_CurrentRequest-OldCurrentRequest,

ImpulseFactor[Index] = Impulse up/down factor from array defined in application,

CurrentError_PosImp = i_CurrentRequest-i_CurrentMeasured and

CurrentError_NegImp = i_CurrentMeasured-i_CurrentRequest

 

, Feedforward term RFF

 

 

, where ff_factor= 0.018

 

 

The following figure shows the current request, measured current and PWM ratio as a function of time.

 

 

 

 

 

The function block includes a startup impulse feature for faster achievement of the target current. The startup impulse has two different modes: automatic and manual mode. Depending on the selected mode, PWM output is momentarily bigger until either the given time is exceeded (manual mode) or the measured current rises enough (automatic mode). The used mode is defined by an input i_AutomaticStartImpulse.

 

Manual mode:

In manual mode the input parameter i_StartImpulseTime defines the startup pulse length.

 

Automatic mode:

In automatic mode the startup pulse is stopped when the measured current is increased enough.

 

• If the current request changes from 0 mA to some current (more than i_ParStep) then the measured current needs to be half (library internal constant) of the target current until the pulse is stopped. In figure above, the request current changes from 0 mA to 700 mA so the measured current needs to be 350 mA until the pulse is stopped.  

• If the current request changes from positive current to some other bigger current (more than i_ParStep) then the measured current needs to increase 1/8 (library internal constant) from the difference of the new current request and the measured current in start point.

• For example, if the request current changes from 200 mA to 600 mA and the measured current is 190 mA when the request current change occurs --> the measured current needs to be 251 mA ((600mA-190mA)/8) until the pulse is stopped.  

 

 

 

The PI controller is activated when current error is small (≤ i_ParStep/2) or if the target current is not reached quick enough.

 

The input parameter i_CurrentChangeSpeed [mA/ms] defines how quick the measured current should change. For example,

• if the target current changes from 0 mA to 700 mA and i_CurrentChangeSpeed = 5 then

• the PI controller is activated if current error > i_ParStep/2 when 140 ms is elapsed since target current change

 

The PI controller is deactivated when a new start-up pulse is started.

 

 

 

The output o_PWMRatio is set to 0 and corresponding error bit is set on:

• i_CurrentRequest > 5000 OR

• i_SupplyVoltMeasured ≤ 0 OR

• Output wire broken or overcurrent situation detected OR

• The input parameters are invalid OR

 

The output wire broken situation is detected when current request is active (i_WireBrokenLimit ≤ i_CurrentRequest) and the measured current is below i_WireBrokenLimit over diagnostic delay time i_DiagnosticDelay.  

The overcurrent situation is detected when the measured current is above i_OverCurrentLimit during diagnostic delay time i_DiagnosticDelay.

 

The output o_PWMRatio is set to 0 immediately if:

• i_Enable is FALSE

 

The error bits are not reset before the rising edge of i_Enable input.

 

 

 

How to adjust controller parameters

For accurate parameter adjusting it is recommended to utilize some CAN bus diagnostic tool, which gives the possibility to monitor graphically CAN signals. The monitored signals are

• i_CurrentRequest,
• i_CurrentMeasured and

• o_PWMRatio

 

These signals should be transmitted to CAN bus as short transmission period as possible (for example, 10 ms) to get a good understanding how the different parameters affect to o_PWMRatio and i_CurrentMeasured.

 

The examples in following sections assumes that

• i_ParameterCount = 20

• meaning that i_pCorrectionParameters, i_pImpulseUpParameters and i_pImpulseDownParameters arrays has 20 indexes

• i_ParStep = 50

• meaning that the first index value in arrays corresponds the current value 50 mA, the second value corresponds the current value 100 mA, ..., the last index value corresponds the current value 1000 mA

 

 

 

 

Rough instructions for adjusting PI controller's P and I terms:

1. Set i_PI_I = 1

2. Increase i_PI_P value (and test with different current requests) until current starts to oscillate. After that decrease i_PI_P value a few digits

3. Increase i_PI_I value (and test with different current requests) until current starts to oscillate. After that decrease i_PI_I value a few digits    

 

The correction parameters i_pCorrectionParameters are used to calculate the basis value to o_PWMRatio. The idea is that with correction parameters the o_PWMRatio value is set immediately close to the "correct" value and the PI controller is only used to fix the minor residual current error.

 

The following example graph shows how to adjust the correction factor value to correspond to current request 400 mA.

 

• Set i_CurrentChangeSpeed = 0 in order PI controller is not activated

• Set i_UseImpulse = FALSE in order start impulse is not in use

• Set i_CurrentRequest = 400 mA

• Analyze graph to decide if correction factor value should be modified

 

 

In many applications it is enough adjust just the correction parameter which corresponds the minimum current and copy that value to all indexes in correction parameter array.

 

 

 

The input i_CurrentChangeSpeed is used to define the time delay before PI controller is activated. i_CurrentChangeSpeed affects always when the change of i_CurrentRequest is  more than i_ParStep between 2 consecutive PVC_AdaptiveController function block instance calls. Typically this situation occurs only in the beginning of movement when current request changes from 0 mA to minimum current.

 

The following graph shows how to adjust the current change speed. The current request i_CurrentRequest changes from 0 mA to 400 mA. i_CurrentChangeSpeed value 20 mA /ms is too big so PI controller is activated too quickly.

 

 

 

 

The input i_pImpulseUpParameters is used to define the startup impulse to o_PWMRatio which will cause that current increases more quickly. i_pImpulseUpParameters affects always when the change of i_CurrentRequest is  more than i_ParStep between 2 consecutive PVC_AdaptiveController FB instance calls. Typically this situation occurs only in the beginning of movement when current request changes from 0 mA to minimum current. Note that i_UseImpulse needs to be true that startup impulse is used.  

 

The following graph shows how to adjust impulse up parameters. i_CurrentRequest changes from 0 mA to 400 mA.

 

• Set i_UseImpulse = TRUE in order start impulse is in use

• Set i_AutomaticStartImpulse = TRUE in order startup impulse length is automatically defined

 

 

 

 

In many applications it is enough adjust just the impulse up parameter which corresponds the minimum current and the rest of indexes in impulse up parameter array can be ignored.

 

 

 

 

The input i_pImpulseDownParameters is used to define the downward impulse to o_PWMRatio which will cause that current decreases more quickly. i_pImpulseDownParameters affects always when the change (decrease) of i_CurrentRequest is  more than i_ParStep between 2 consecutive PVC_AdaptiveController FB instance calls. In many typical applications this do not occur ever so impulse down parameters can be ignored. Note that i_UseImpulse needs to be true that downward impulse is used.

 

The following graph shows how to adjust impulse down parameters. i_CurrentRequest changes from 700 mA to 500 mA.

 

• Set i_UseImpulse = TRUE in order start impulse is in use

• Set i_AutomaticStartImpulse = TRUE in order startup impulse length is automatically defined

 

 

In many applications the values in impulse down parameter array can be ignored. However, the impulse down array needs always  to be defined and given to the PVC_AdaptiveController as a input.

 

 

 

 

Source file topic100532.htm

Last updated 13-Jun-2024